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DTC P0171, P0172, P0174, or P0175

DTC P0171, P0172, P0174, or P0175

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptors

DTC P0171

Fuel Trim System Lean Bank 1

DTC P0172

Fuel Trim System Rich Bank 1

DTC P0174

Fuel Trim System Lean Bank 2

DTC P0175

Fuel Trim System Rich Bank 2

Circuit/System Description

The engine control module (ECM) controls a Closed Loop air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage, and adjusts the fuel delivery based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The long term fuel trim values change in response to changes in the short term fuel trim. The long term fuel trim makes coarse adjustments to fueling in order to adjust and restore control to short term fuel trim. The ideal fuel trim values are around 0 %. A positive fuel trim value indicates that the ECM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition.

Conditions for Running the DTC


• DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0178, P0179, P0201-P0206, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0275, P0277, P0300-P0306, P0442, P0443, P0446, P0449, P0451-P0455, P0496, P0506, P0507, P1248, P1249, P124A, P124B, P124C, P124D, P2147, P2148, P2150, P2151, P2153, P2154, P2156, P2157, P216B, P216C, P216E, P216F, P2227-P2230, P2269 are not set.

• The engine is in Closed Loop status.

• The catalyst monitor diagnostic intrusive test, post 02 diagnostic intrusive test, device control, and EVAP diagnostic Tank Pull Down test are not active.

• The engine coolant temperature (ECT) is between -38 and +150°C (-36 and +302°F).

• The intake air temperature (IAT) is between -38 and +150°C (-36 and +302°F).

• The manifold absolute pressure (MAP) is between 5-255 kPa (1.45-37 psi).

• The engine speed is between 400-6,600 RPM.

• The mass air flow (MAF) is between 0.5-510 g/s.

• The barometric pressure (BARO) is greater than 70 kPa (10.2 psi).

• The fuel level is greater than 10 %.

• This diagnostic runs continuously when the above conditions have been met.


Conditions for Setting the DTC


• The average long term fuel trim weighted average value is greater or less than a calibrated value.

• The above condition is present for approximately 3 min after the Conditions for Running the DTC have been met.


Action Taken When the DTC Sets

DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.

Diagnostic Aids


• Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.

• The normal Short Term Fuel Trim and Long Term Fuel Trim parameters should be between +10 and -10 % with 0 % the optimum, with the engine running at operating temperature.

• An HO2S will not cause this DTC to set without the occurrence of the circuit related HO2S DTCs. Do not replace an HO2S to address this DTC.

• Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.

• A MAF sensor condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor parameters will appear to be within range.

• Inspect the air filter for being the correct one for this application. Make sure that the engine oil fill cap is in place and that it is tight. Verify that the engine oil dip stick is fully seated.

• Certain aftermarket air filters may cause a DTC to set.

• Certain aftermarket air induction systems or modifications to the air induction system may cause a DTC to set.

• Certain aftermarket exhaust system components may cause a DTC to set.


Reference Information

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification


1. Check the DTC information with a diagnostic tool. DTC P0171, P0172, P0174, or P0175 should not be set.

2. Engine running, observe the DTC information with a scan tool. Verify there are no HO2S DTCs set.

3. If any HO2S DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

4. Ignition ON, observe the manifold absolute pressure MAP sensor parameter. The MAP sensor pressure should be within the range specified for your altitude above sea level. Refer to Altitude Versus Barometric Pressure .

5. If not the specified range, refer to DTC P0106 (LF1) .

6.
Note

EVAP purge enablement may cause the Fuel Trim to be momentarily outside the normal range.


Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term Fuel Trim parameter with a scan tool. The value should be between -20 % and +20 %.

7. If not the specified range, inspect for the following:

• A mass air flow (MAF) sensor signal that is skewed-If the Short Term Fuel Trim parameters for both banks changes greater than 20 % when the MAF sensor is disconnected, refer to DTC P0101 (LAU) DTC P0101 (LF1) .

• Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Special Tool) Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) .

• Missing, restricted, or leaking exhaust components-Refer to Symptoms - Engine Exhaust .

• Malfunctioning fuel injectors-Refer to Fuel Injector Solenoid Coil Test (LAU) Fuel Injector Solenoid Coil Test (LF1, LFW) .

• Vacuum hoses for splits, kinks, and improper connections

• Insufficient fuel in the tank

• Low fuel pressure-Refer to Fuel System Diagnosis (LF1 China) Fuel System Diagnosis (LF1 Except China) Fuel System Diagnosis (LAU China) Fuel System Diagnosis (LAU Except China) .

• Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings.

• The air induction system and the air intake ducts for leaks, or for a missing air filter element

• A cracked EVAP canister

• Evaporative pipes obstructed or leaking

• The crankcase ventilation system for leaks

• A mass air flow (MAF) sensor signal that is skewed-If the Short Term Fuel Trim parameters for both banks changes greater than 20 % when the MAF sensor is disconnected, refer to DTC P0101 (LAU) DTC P0101 (LF1) .

• Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Special Tool) Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) .

• Missing, restricted, or leaking exhaust components-Refer to Symptoms - Engine Exhaust .

• Malfunctioning fuel injectors-Refer to Fuel Injector Solenoid Coil Test (LAU) Fuel Injector Solenoid Coil Test (LF1, LFW) ,

• The air intake duct for being collapsed or restricted

• Excessive fuel pressure - Refer to Fuel System Diagnosis (LF1 China) Fuel System Diagnosis (LF1 Except China) Fuel System Diagnosis (LAU China) Fuel System Diagnosis (LAU Except China)

• The air filter for being dirty or restricted

• Objects blocking the throttle body

• The evaporative emissions control system for improper operation

• Excessive fuel in the crankcase-Change the oil as necessary.

8. If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical .

9. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.